The present invention relates to a liquid crystal display (LCD) a heat resistant polymer composition and an alignment layer using the heat resistant polymer composition.
In general, a liquid crystal molecule has an intermediate property of a liquid and a solid, the fluidity of a liquid and the optical property of a solid, and can be changed in its optical anisotropy with an electric field or heat. A liquid crystal display (LCD) utilizes such properties and is typically used as a flat-panel display.
FIG. 1 is a schematic sectional view of a general LCD, in which transparent electrodes 3 and 3' composed of indium tin oxide (ITO) are respectively formed on upper and lower glass substrates 2 and 2'. Insulating layers 4 and 4' and alignment layers 5 and 5' for aligning liquid crystals are sequentially formed on the transparent electrodes 3 and 3'. Spacers 6 are disposed between the alignment layers 5 and 5' with a cell gap. A liquid crystal material is injected into the cell gap to form a liquid crystal layer 7. Polarizing plates 1 and 1' for polarizing incident and transmittant light are provided on the exterior of substrates 2 and 2'.
FIG. 2 shows a directional relationship between liquid crystal molecules and an alignment surface (substrate), in which a pre-tilt angle refers to the angle formed by the substrate surface and a liquid crystal director. An alignment layer must be formed by employing an appropriate alignment material or using an appropriate alignment method so that the pre-tilt angle of the liquid crystal can be adjusted to within a proper range, which is essential in improving the display performance of the LCD.
To form an alignment layer, a rubbing treatment has been generally used, that is, a polymer resin film such as a polyimide film is formed on a substrate where an electrode is formed and then the film is rubbed with a piece of cloth.
According to the rubbing treatment, an alignment layer composition including a polyimide resin is coated on the where an electrode layer formed and is then thermally treated at 200.degree..about.250.degree. C. for about 1 hour and subjected to rubbing to form an alignment layer. To form a liquid crystal layer, a spacer is then coated on the substrate where the alignment layer is formed and the upper and lower substrates are sealed with a predetermined cell gap. Thereafter, a liquid crystal composition is injected into the cell gap and is thermally treated again at about 100.degree. C. However, the alignment layer may be damaged by the heat treatment which disadvantageously changes the pre-tilt angle or alignment degree, resulting in deterioration of LCD performance.